Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers. Generally speaking, a power amplifier amplifies an audio signal by taking energy from a power supply and controlling an audio output signal to match an input signal shape but with a larger amplitude. Although many amplifier architectures (e.g., Class A, Class B, and Class AB amplifiers) provide for only a single power supply for a power amplifier, some architectures provide for at least two supply voltages for powering a power amplifier, in order to achieve greater power efficiency over single or constant power supply voltage architectures.
One example of a multi-supply voltage amplifier is a Class G amplifier. A Class G amplifier may provide two or more power rails at different voltages and switch between them as the signal output approaches each level. Thus, a Class G amplifier may increase efficiency by reducing the wasted power at output driving transistors of the amplifier. In some instances, a Class G amplifier may be combined with a Class D amplifier to create a Class DG amplifier. A Class DG amplifier may use pulse-width modulation to produce a rail-to-rail digital output signal with a variable duty cycle as a pre-driver signal to an output driver, as is typical with Class D amplifiers. However, as opposed to a Class D amplifier, a Class DG amplifier may use a multi-level output stage which senses a magnitude of the audio output signal and switches between power supplies based on the output magnitude.
Another example of a multi-supply voltage amplifier is a Class H amplifier. A Class H amplifier may be similar to a Class G amplifier, except that instead of selecting among a plurality of voltage rails, a Class H amplifier may have an infinitely variable voltage supply rail. In order to provide such an infinitely variable voltage supply rail, the output supply rail may be modulated such that the rail is only slightly larger than a magnitude of the audio output signal at any given time. For example, switched-mode power supplies may be used to create the output signal-tracking voltage rails.
However, in Class G, Class DG, and Class H amplifiers, when modifying an output voltage, audible audio artifacts (e.g., “pops” and “clicks”) may be heard by a listener of an audio device unless measures are taken to reduce or eliminate such audio artifacts.